package QuickSort;

import MergeSort.ArrayGenerator;
import MergeSort.SortingHelper;

import java.util.Arrays;
import java.util.Random;

public class QuickSort  {

    private QuickSort(){}

    public static  <E extends Comparable<E>> void sort(E[] arr){
        sort(arr, 0, arr.length - 1);
    }

    private static <E extends Comparable<E>> void sort(E[] arr, int l, int r){

        if(l >= r) return;

        int p = partition(arr, l, r);
        sort(arr, l ,p - 1);
        sort(arr, p + 1, r);
    }

    private static <E extends Comparable<E>> int partition(E[] arr,int l, int r){

        // 生成[l, r] 之间的随机索引
        int p = l + (new Random()).nextInt(r - l + 1);
        swap(arr, l , p);

        // arr[l + 1...j] < v; arr[j +1 ...i] >= v
        int j = l;
        for(int i = l + 1; i <= r; i++)
            if(arr[i].compareTo(arr[l]) < 0){
                j++;
                swap(arr, i, j);
            }

        swap(arr, l, j);
        return j;
    }

    public static  <E extends Comparable<E>> void sort2ways(E[] arr){
        sort2ways(arr, 0, arr.length - 1);
    }

    private static <E extends Comparable<E>> void sort2ways(E[] arr, int l, int r){

        if(l >= r) return;

        int p = partition2(arr, l, r);
        sort2ways(arr, l ,p - 1);
        sort2ways(arr, p + 1, r);
    }

    private static <E extends Comparable<E>> int partition2(E[] arr,int l, int r){

        // 生成[l, r] 之间的随机索引
        int p = l + (new Random()).nextInt(r - l + 1);
        swap(arr, l , p);

        // arr[l+1...i-1] <= v  arr[j+1...r] >= v
        int i = l + 1, j = r;
        while (true){

            while (i <= j && arr[i].compareTo(arr[l]) < 0)
                i++;
            while (j >= i && arr[j].compareTo(arr[l]) > 0)
                j--;

            if(i >= j) break;

            swap(arr, i, j);
            i++;
            j--;
        }
        swap(arr, l ,j);
        return j;
    }

    public static  <E extends Comparable<E>> void sort3ways(E[] arr){
        Random rnd = new Random();
        sort3ways(arr, 0, arr.length - 1, rnd);
    }

    private static <E extends Comparable<E>> void sort3ways(E[] arr, int l, int r,Random rnd){

        if(l >= r) return;
        // 生成[l, r]之间的随机索引
        int p = l + rnd.nextInt(r - l + 1);
        swap(arr, l, p);

        // arr[l + 1, lt] < v, arr[lt + 1, i - 1] == v, arr[gt, r] > v
        int lt = l, i = l + 1, gt = r + 1;
        while (i < gt){
            if (arr[i].compareTo(arr[l]) < 0){
                lt ++;
                swap(arr, i, lt);
                i ++;
            }
            else if(arr[i].compareTo(arr[l]) > 0){
                gt --;
                swap(arr, i, gt);
            }
            else{//==
                i++;}
        }
        swap(arr, l, lt);
        // arr[l, lt - 1] < v, arr[lt, gt - 1] == v, arr[gt, r] > v
        sort3ways(arr, l ,lt - 1, rnd);
        sort3ways(arr, gt, r, rnd);
    }

    private static <E> void swap(E[] arr, int i, int j){
        E t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;

    }

    public static void main(String[] args) {

        int n = 1000000;

        Integer[] arr = ArrayGenerator.generateRandomArray(n, n);
        Integer[] arr2 = Arrays.copyOf(arr, arr.length);
        Integer[] arr3 = Arrays.copyOf(arr, arr.length);


        SortingHelper.sortTest("QuickSort", arr);
        SortingHelper.sortTest("QuickSort2Ways", arr2);
        SortingHelper.sortTest("QuickSort3Ways", arr3);
    }
 }
